In copending applications Ser. Nos. 378,285 and 400,636 assigned to the assignee of the present application, an engine control system is disclosed which utilizes a computer or microprocessor. The system disclosed is of the so-called EAC type wherein driver fuel command signals derived from actuation of the accelerator pedal are supplied to the computer, which then controls a throttle mechanism to provide the precise amount of air necessary to produce an optimum air-fuel ratio. Electronically, insofar as components are concerned, the system includes a first printed circuit board on which are mounted the elements comprising the computer or CPU unit, a second or power supply board that handles all of the power control elements of the system, a driver command signal generator and various pressure sensors adapted for connection with certain engine locations which are required for throttle valve control inputs. All of the aforesaid components must be packaged in a housing that is compact, that is readily mountable in an accessible location in the engine or passenger area, that will dissipate heat and provide an acceptable temperature environment for all system elements under varying conditions, and that will provide a high degree of protection for these elements and thus assure safety and reliability for the engine.
Most automotive computers in use today are relatively simple devices which dissipate small amounts of heat. The trend, however, is toward more complex computers which perform more control functions. Each control function requires an actuator of some kind (e.g. a motor, a fuel injector, or a light bulb). In order to power the actuator, a solid state switch of some kind must be used. These switches are not 100% efficient, therefore some of the power they use is lost in the form of heat. Then too, the computer circuitry utilizes a fixed voltage (often 5 volts) to power its circuitry. The voltage regulation circuits usually dissipate considerable heat.
To dissipate heat and maintain environmental temperature within limits, the heat-generating devices must be held in close contact to a large heat conducting structure usually called a heat sink. Traditionally, the attachment of the heat-generating devices is by means of screws or rivets. Such attachment is costly in terms of time and materials, and removal is often more difficult.
The requirements for the computer enclosure are several, therefore. First, a considerable amount of power must be dissipated in the form of heat. Often amounts approaching 100 watts must be rejected. Second, the enclosure must protect the computer circuitry from the high temperatures associated with the power producing circuits. Third, the computer must be protected from the electrical noise which is often generated by the power switching devices. Fourth, a rigid case or enclosure must be provided which protects the computer from trauma and the elements. Fifth, the power-generating devices in the system must be connected to the heat sink quickly and reliably without individually attaching each device.
Another problem which arose with automotive engine control systems heretofore devised was in providing reliable and accurate driver fuel command signals as well as proper signals from other pressure sensors.
In conventional vehicles powered by a gasoline internal combustion engine, the driver's right-most pedal influences the power output of the engine. Generally, the pedal is connected via a cable or rod to a throttle plate which is located in the intake air stream. Depression of the pedal allows more air to enter the engine. Heretofore, the engine was fitted with a carburetor, and the increased airflow caused increased fuel to flow into the air stream and therefore increased engine power. If the engine was fitted with a conventional fuel injection system, an airflow sensor or manifold pressure sensor detected the increased airflow and caused more fuel to be injected into the air stream. In some fuel injection systems, a sensor located at the throttle plate sensed the angle of the throttle (and therefore the driver pedal position). This signal was used to detect changes in the driver's pedal position in order that the fuel injection system could more quickly respond to changes in the pedal position and therefore reduce the tendency to go lean upon acceleration. It is important to note that this pedal sensor was not used as the sole basis of adding fuel to the engine.
In an EAC system, the driver's right-most foot pedal is not connected to the throttle. Rather, the driver's pedal position provides an input to a computer. The computer determines the amount of fuel to be added and actuates fuel injectors. The computer also determines the amount of air which should be admitted to the engine and commands a motor-driven throttle plate in the air intake manifold to the correct position. Unlike the conventional (EFC) fuel injection system in which the driver's pedal position controls the throttle directly and the pedal sensor only measures the change in position, in the case of EAC, the driver's pedal position is resolved by the computer solely on the basis of the sensor. The driver's pedal position (called the driver fuel command) determines the power output of the engine. The driver fuel command is therefore an extremely important signal whose correct resolution is vitally necessary to proper engine operation and performance.
If the driver fuel command sensor is located at some distance from the computer, then the driver fuel command signal must be transmitted through wires via an electrical signal. If the electrical signal were modified in such a way that the computer would incorrectly determine the driver's pedal position, then serious damage or injury could occur. If, for example, the wires carrying the driver fuel command signal were traumatized, the result could be that the computer would misinterpret the driver's pedal position. In addition, a sensor which is separated from the computer must be shielded from dirt, dust, moisture, and electrical noise, and the electrical wires connecting the sensor and the computer must be shielded from electrical noise. Provisions must also be taken to prevent unauthorized tampering with the wires or installation of "hand throttles" which violate motor vehicle laws.
The location of various required engine sensors and their proper connection with the engine control system is also important to the smooth and reliable operation of the system.
In some fuel-injected automobiles, a pressure sensor (also called a pressure transducer) measured the absolute pressure within the engine manifold. An electrical signal was produced by the transducer which was in some manner proportional to manifold pressure. An electrical circuit which might contain a computer used the electrical signal to measure airflow into the engine. The pressure transducer was typically mounted on or near the engine, and an electrical signal carried the pressure information to the electrical control unit.
In an EAC system which measures airflow by measuring pressure drop across the throttle, a pressure transducer is needed to allow the control computer to determine pressure drop. Typically, a differential pressure transducer is used which is designed to measure a pressure difference. Pressure drop across the throttle measures the volume flow of air past the throttle. Because the air/fuel ratio of the engine is extremely important, and because the air/fuel ratio is based upon the mass of fuel and air and not the volume of fuel and air, a correction must be made to to the measure of the volume flow of air past the throttle. Measuring the temperature of the air and the absolute pressure of the air allows a volume-to-mass-flow correction to be made.
Thus, an EAC system, as described, requires two pressure transducers, one to measure the differential pressure across the throttle and one to measure the absolute pressure of the air above the throttle. Using prior techniques, both transducers were mounted on or near the engine, and the pressure signals furnished to the engine control computer sensors were required to be capable of withstanding high under-hood temperatures. Second, the sensors were required to be protected from the electrical noise of the high voltage ignition system. Third, the interconnecting wires were required to be shielded from electrical noise. Fourth, the sensors needed to be protected from dirt, dust, vibration, and moisture. Fifth, a connector, was required to allow the pressure sensor to be installed onto the end of an electrical cable harness.
It is therefore a general object of the present invention to provide a single housing or enclosure for an automotive engine control system that solves the aforesaid problems and fulfills the aforesaid requirements.
Another object of the invention is to provide an improved housing for an electronic engine control system that is easy to assemble and yet provides firm reliable electrical connections between components.
Another object of the invention is to provide an electronic engine control system with an improved housing that will dissipate at a relatively high rate the heat produced internally by power-consuming electrical elements of the system, thereby widening the range of locations where the housing can be installed in proximity to the engine.
Another more specific object of the invention is to provide an enclosure with an automotive engine control system including a computer which affords protection from excess heat as well as from extraneous, outside forces and electrical noise that could otherwise damage the computer or cause erroneous signals.
Still another object of the invention is to provide an automotive fuel control system of the EAC type that will enable its computer to determine, with a high degree of accuracy and reliability, the position of the driver's fuel command pedal.
Another object of the invention is to provide an automotive engine control system with an enclosure having a driver command sensor mounted within the enclosure adjacent the system electronics, thereby making the sensor more tamper proof, and protecting it from external forces so that it is more reliable.
Yet another object of the invention is to provide an electronic engine control system wherein all of the systems electronics, the driver command sensor and also manifold and absolute pressure sensors are enclosed within a single housing.
A further object of the present invention is to provide an electronic engine control system with a housing or enclosure that accommodates the major elements thereof in a manner that is particularly well adapted for ease and economy of manufacture.
Another object of the invention is to provide a compact housing for elements of an electronic engine control system, including its electronic components as well as certain sensors, which is particularly well adapted for ease of installation and accessability for testing and maintenance.